Whisker-reinforced Composites Research Articles

Reinforcement mechanisms and current research status of silicon carbide whisker-reinforced composites: A comprehensive review

Abstract In recent decades, with the advancement of micro-electro-mechanical systems technology, traditional materials have become insufficient to meet the demands of cutting-edge technology for various material properties. Composites have attracted widespread attention as an effective and viable solution. Silicon carbide whiskers (SiCw) have emerged as excellent reinforcements due to their high thermal conductivity, low thermal expansion coefficient, high melting point, superior mechanical properties, and high chemical stability. This article provides a comprehensive review of the reinforcement mechanisms and current research state of SiCw-reinforced composites. The reinforcement mechanisms include mainly grain refinement, load transfer, and crack bridging. The composites are categorized based on the type of the matrix: ceramic-based, metal-based, and polymer-based composites. The influence and parameter performance of the reinforcement mechanism on SiCw-reinforced composite materials with different matrices vary. However, the key to improving SiCw-reinforced composites lies in understanding the interplay of properties between the matrix and the reinforcement, as well as the ordered and regular distribution and binding at the interface. Finally, the current state and limitations of SiCw-reinforced composites are summarized, and future development trends are discussed. This article represents a great contribution to the future applications of SiCw-reinforced composite materials.

Mechanical anisotropy in polymer composites produced by material extrusion additive manufacturing

Extrusion-based additive manufacturing technologies, such as direct ink writing of filled polymer resins, have shown a great potential for the development of printed components with superior structural and functional properties. However, the associated extrusion process induces preferred orientation on high-aspect-ratio filler materials as they extrude through the deposition nozzle, causing strong mechanical anisotropy in printed components. Printing-induced anisotropy is a critical issue that complicates the straightforward design of additively manufactured components. The goal of this work is to gain a better understanding of the anisotropy in printed polymer composites by investigating the effects of filler morphology and print parameters on the mechanical properties of printed composites. Inks are formulated using fumed silica particles or nanoclay platelets as the primary viscosifying agent, and silicon carbide (SiC) whiskers as the primary mechanical reinforcement. Mechanical anisotropy is characterized via 3pt-flexural tests for epoxy ink formulations utilizing fumed silica or nanoclay, with or without SiC whiskers, and printed at three different print speeds, using three different nozzle sizes. Orientation of nanoclay is also characterized using small- and wide-angle x-ray scattering. Results show that smaller nozzle diameters and higher deposition rates lead to greater anisotropy when nanoclay or SiC fillers are utilized, while the use of fumed silica alone results in mechanical behavior that is independent of print parameters and print path. Superior flexure strength values up to 215 MPa are obtained with SiC whisker-reinforced composites when tested parallel to the print direction.

An analytical model for elastic modulus calculation of SiC whisker-reinforced hybrid metal matrix nanocomposite containing SiC nanoparticles

In the present work, elastic modulus of a hybrid aluminum matrix nanocomposite (HAMNC) reinforced with silicon carbide (SiC) whiskers and SiC nanoparticles is analyzed. To this end, a new multi-scale analytical model is developed to calculate the effective elastic modulus of the HAMNC. The SiC nanoparticle aggregation into the HAMNC, frequently encountered in real engineering situations, is simulated. The elastic modulus of HAMNC estimated by the analytical micromechanical model is compared with that directly measured by the experimental method and a good agreement is found between the two sets of results. The effects of volume fraction, aspect ratio and dispersion type of SiC whiskers as well as volume fraction, size and aggregation degree of SiC nanoparticles on the HAMNC elastic modulus are extensively investigated. It is found that the elastic modulus of the SiC whisker-reinforced composite is significantly improved due to the addition of SiC nanoparticles. The results show that the nanoparticle aggregation has a damaging effect on the HAMNC elastic modulus. It is observed that the HAMNC elastic modulus can be enhanced by (i) increasing SiC content, (ii) aligning the SiC whiskers, (iii) increasing the SiC whisker aspect ratio (iv) decreasing the SiC nanoparticle size and (v) uniform dispersion of SiC nanoparticles into the hybrid nanocomposite. The reported results by means of the analytical model can be actually useful to guide design of general hybrid metal matrix nanocomposites with superior effective properties.

Reinforcing polypropylene with calcium carbonate of different morphologies and polymorphs

Abstract The influence of calcium carbonate (CaCO3) with different polymorphs (calcite and aragonite) and morphologies (granular and rod-like) on mechanical and crystallization properties of polypropylene (PP) was investigated. Meanwhile, these CaCO3 fillers coated with oleic acid were added in different contents to PP. The results indicate that the tensile strength, flexural strength, modulus, and crystallization property of the filler-treated samples are improved, but the impact strength decreased. The crystallinity of the composites is higher than that of neat PP. Moreover, in the rod shape filler-treated sample, in both whisker species, the mechanical properties of composites are superior to the particles filled. Differential scanning calorimetry, X-ray diffraction, and mechanical tests display that calcite whisker-reinforced composite has higher crystallization enthalpy, melting enthalpy, degree of crystallinity, and mechanical properties than aragonite whiskers and calcite particles filled composites.

Numerical predictions of the mechanical properties of NT-ZnOw reinforced composites

A new method to generate a three-dimensional (3D) nanoscale tetrapod-shaped zinc oxide whisker (NT-ZnOw) with spatial random distribution is proposed, and a corresponding program is developed. A whisker-generating program is combined with finite element method to build a 3D finite element model that can predict the mechanical properties of NT-ZnOw/resin composites. A 3D finite-element unit cell is adopted and subjected to periodic displacement boundary conditions to explore the equivalent mechanical properties of the NT-ZnOw/resin composites. A micromechanics finite element model of the NT-ZnOw reinforced composites containing various volume fractions of NT-ZnOw is also developed. Effects of different volume fractions and aspect ratios of the whisker on the stiffness of the composites are investigated. These parameters can be used in the microscopic prediction and analysis to determine the mechanical properties of whisker-reinforced composites with multivariate and random distribution of the whiskers. The numerical and theoretical predictions are in good concordance.

Strength and toughness improvement in a C/SiC composite reinforced with slurry-prone SiC whiskers

The present paper reports on the strength and toughness improvement in carbon-fiber reinforced silicon carbide (C/SiC) composites as a result of slurry-prone SiC whisker presence at varying concentrations. For whisker contents of 5 and 15wt%, the SiCw–C/SiC composite flexural strength was found to increase by 98.5% and 64.3%, respectively, from the whisker-free case while work of fracture increased by 209.8% and 179.0%, respectively. For the same respective whisker concentrations, porosity was found to decrease by 4.9% and increase by 19.4% compared to plain samples. The composites’ interlaminar shear strength exhibited similar non-monotonic response with the property value for 5wt% whisker-reinforced composites being higher by 12.5MPa than the plain specimens and higher by 14.9MPa than the composites with 15wt% whisker content. Fiber pullout in SiCw–C/SiC composites was considerably more prominent than in the whisker-free material and the corresponding mean pullout lengths were significantly longer than in plain specimens. The improvements in strength and toughness were attributed to the energy dissipation mechanisms of crack deflection, whisker bridging and pullout coupled with conventional fiber pullout.

Machinability of Short Potassium Titanate Fiber Reinforced Aluminum Alloy Composites Fabricated by Squeeze Casting

Short potassium titanate fibers were selected as the reinforcements to obtain the machinable aluminum alloy composites. The composites were fabricated by squeeze casting, and the turning machinability of the composites was investigated. The whisker-reinforced composites were also fabricated to compare their properties with the fiber-reinforced composites. The cutting force was lowered by the reinforcement, and that of the fiber-reinforced composite was lower than that of the whisker-reinforced composites. The roughness of the machined surface was lowered by the reinforcement. This result and the in situ observation of cutting process indicate that the reinforcements in the composite suppress the formation of the built-up edge. Continuous chips were formed after cutting the unreinforced alloy, while serrated chips were formed after cutting the composites. Under the standard condition for the finishing cut of nonferrous metals, the composite can be machined for a long time without changing the carbide tool.

Hybrid Effect on Whisker Orientation Dependence of Composite Strength of Aluminum Cast Alloy Reinforced by Al2O3 Whiskers and SiC Particles

The hybrid effect on the orientation dependence of the composite strength of an aluminum cast alloy reinforced by Al2O3 whiskers and SiC particles is studied experimentally and numerically. Two types of specimens are prepared for monotonic bending tests. The longitudinal specimen orientation (maximum stress direction) is parallel to or normal to randomly oriented whiskers in plane. The monotonic strength is 18% higher when the hybrid metal matrix composite (MMC) is subjected to an external load parallel to the random whisker orientation in plane than when the load is perpendicular to the whisker orientation. The whisker orientation dependence of composite strength in hybrid composite is weaker than that in whisker-reinforced composite. On the fracture surface of the specimen loaded along the direction parallel to the random whisker orientation in plane, most whiskers are broken while many de-bonded interfaces between the whiskers and matrix are observed on the fracture surface of the specimen loaded along the direction perpendicular to the whisker orientation. To characterize the hybrid effect on the whisker orientation dependence of composite strength, a three-dimensional hybrid composite unit cell model including one whisker and a few particles under a periodic boundary condition is developed using the finite element method. The hybrid composites have higher whisker stress than whisker-reinforced composite when subjected to an external load parallel to the whisker orientation if these composites have the same total volume fraction of reinforcement and the particles are distributed randomly. Under an external load perpendicular to the whisker orientation, the interface stress of hybrid composites is lower than that of whisker-reinforced composite. As a result, the strength difference for parallel and perpendicular loading conditions of the hybrid composites is smaller than that of whisker-reinforced composite. Thus, the weak whisker orientation effect in the hybrid composites is due to a change in microscopic stress distribution induced by interaction between whiskers and particles.

Load partitioning in honeycomb-like silicon carbide aluminum alloy composites

A 50/50 vol.% Al/SiC composite was made via melt infiltration of an aluminum alloy into a porous beech wood-derived SiC preform. The honeycomb-like composite microstructure consisted of an interconnected SiC phase surrounding discrete Al “fibers” aligned in the growth direction of the beech wood. High energy synchrotron X-ray diffraction was used to measure the volume averaged lattice strains in both the SiC and Al phases during in situ compressive loading up to an applied stress of −530 MPa. Load transfer from the Al to the SiC was observed, and the Al yielded at an applied stress of above −213 MPa. The elastic behavior of the composite was modeled with both an isostrain rule of mixtures calculation and variational bounds for the effective elastic modulus. Furthermore, calculations of the von Mises effective stress of the SiC and Al phases showed that the wood-derived SiC was a more effective reinforcement than either SiC particle- or whisker-reinforced composites.

Investigation into hemp fiber- and whisker-reinforced soy protein composites

Whiskers, designated as W, were prepared from hemp fibers. Both fibers and whiskers were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis. Scanning electron microscopy and transmission electron microscopy were used to evaluate the dimensions of the fibers and whiskers, respectively. By incorporating different weight fraction of the fibers and whiskers into soy protein isolate, we prepared two different composites designated as SC and SC-W, respectively. Thiodiglycol was used as a plasticizer for the preparation of composites. The SC and SC-W composites were characterized and compared in terms of mechanical properties, volume fraction of porosity, and water uptake. The results indicated that there was not much significant difference in the properties of the composites. In fact, mechanical properties of fiber-reinforced composites were higher than whisker-reinforced composites at optimum weight fractions. This study can give us the idea about the judicious use of fibers or whiskers as reinforcement materials.

Effect of extrusion on the thermal expansion behavior of Al 18B 4O 33 whisker–Mg composites

The thermal expansion behaviors of AZ91D alloy and Al18B4O33 whisker (w)–AZ91D fabricated by different techniques were investigated at 30–300 °C. The results indicate that these behaviors were greatly influenced by extrusion forming, which reduced the coefficients of thermal expansion (CTE) of AZ91D and Al18B4O33w–AZ91D and resulted in negative strain. The residual stresses could be eliminated by thermal cycling. The CTE of the whisker-reinforced composites could be predicted accurately by micromechanical modelling.

Microstructure and properties of ceramics and composites joined by plastic deformation

A review is presented of the design of suitable materials systems for joining by high-temperature plastic deformation, details of the joining techniques, microstructures and properties of the resulting composite bodies, and prospects and limitation for this type of joining technology. Joining parameters and resulting forms are discussed for Al 2O 3/mullite particulate composites, Y 2O 3-stabilized ZrO 2 particulate/Al 2O 3 particulate and whisker-reinforced composites, hydroxyapatite bioceramics, La 0.85Sr 0.15MnO 3 electronic ceramics, MgF 2 optical ceramics, and Ni 3Al intermetallics. Results are contrasted with those obtained by other methods of joining brittle, high-temperature materials, with special focus on durability and mechanical properties.

Fusion and friction stir welding of aluminum-metal-matrix composites

Microstructure evolutions and degradations of aluminum-metal-matrix composites during fusion welding were studied and compared with thermodynamic calculations. In fusion welds of Al2O3-reinforced composites, the decomposition of Al2O3 was observed. In fusion welds of SiC whisker-reinforced composites, the decomposition of SiC to Al4C3+Si by reaction with molten aluminum occurred. These phenomena led to unacceptable fusion welds in aluminum metal-matrix composites. Successful welds were produced in the same composites by friction stir welding (FSW). Significant reorientation of SiC whiskers close to the boundary of the dynamically recrystallized and thermomechanically affected zone (TMAZ) was observed. The small hardening in the dynamically recrystallized region was attributed to the presence of dislocation tangles in between SiC whiskers.

The low velocity impact loading of Al2O3/SiC whisker reinforced ceramic composite

Ceramic composite materials possess both low toughness and low impact resistance. However, the incorporation of ceramic whiskers into the microstructure of ceramic matrix has been shown to produce a ceramic composite with improved toughness and greater strength. This paper studies both experimentally and theoretically the dynamic behavior of SiCw/Al2O3 ceramic composites under low velocity impact loading. The main objective of this paper is to determine the effects of dynamic flexural stresses on impact resistance, failure modes, and toughening mechanisms of whisker-reinforced composites. To accomplish this objective, several samples of this composite material using different SiC whisker volume fractions were designed and fabricated, and then tested at low-velocity impact loading. A theoretical solution to the transverse impact problem of whisker-reinforced ceramic composite plates by striking these plates with solid projectiles, at low impact velocity was formulated, and its predictions are compared to impact test results. In addition, correlations between impact test results and these composites’ material properties are also included in this study.

The low velocity impact loading of Al2O3/SiC whisker reinforced ceramic composite

Ceramic composite materials possess both low toughness and low impact resistance. However, the incorporation of ceramic whiskers into the microstructure of ceramic matrix has been shown to produce a ceramic composite with improved toughness and greater strength. This paper studies both experimentally and theoretically the dynamic behavior of SiCw/Al2O3 ceramic composites under low velocity impact loading. The main objective of this paper is to determine the effects of dynamic flexural stresses on impact resistance, failure modes, and toughening mechanisms of whisker-reinforced composites. To accomplish this objective, several samples of this composite material using different SiC whisker volume fractions were designed and fabricated, and then tested at low-velocity impact loading. A theoretical solution to the transverse impact problem of whisker-reinforced ceramic composite plates by striking these plates with solid projectiles, at low impact velocity was formulated, and its predictions are compared to impact test results. In addition, correlations between impact test results and these composites’ material properties are also included in this study.

Effect of NiO coating of whisker on tensile strength of aluminum borate whisker-reinforced aluminum composite

After NiO coating of aluminum borate whisker, the whisker-reinforced aluminum composite was fabricated by the squeeze casting technique. The effects of surface coating on the interface reaction and microstructure of the composite were investigated using transmission electronic microscope. The results indicate that the NiO on the whisker surface can react with the aluminum matrix during T4 treatment, and the degree of the reaction increases with the T4 treatment time increasing. The interfacial reaction affects obviously the tensile strength of the composite, and the suitable degree of the interfacial reaction can be found for the ultimate tensile strength.

Stress Corrosion Cracking and Hydrogen Embrittlement of Whisker-Reinforced Aluminum Composites

Abstract Stress corrosion cracking (SCC) in an 3.5% sodium chloride (NaCl) aqueous solution, hydrogen-induced cracking (HIC) during dynamic charging, and hydrogen embrittlement (HE) after precharging of whisker-reinforced aluminum composites were studied. For all four aluminum composites with the whisker direction perpendicular to the normal stress, SCC occurred but no SCC occurred if the whisker direction of Al18B4O33/Al was parallel to the normal stress. The threshold stress intensity of SCC (KISCC), measured using double cantilever beam (DCB) specimens, was (0.94 to 0.70)KIC, where KIC is the fracture toughness. The susceptibility to SCC, measured by slow strain rate test (SSRT), was 24% for SiC/Al and 13% for Al18B4O33/Al. The susceptibility to HE of Al18B4O33/Al was 44%. HIC occurred during dynamic charging under Mode II loading and the threshold stress intensity was KIIH = 0.85KIIC for SiC/Al and 0.88 KIIIC for Al18B4O33/Al, respectively. The results show that the existence of the whisker/Al interfa...

Hydroxyapatite whiskers provide improved mechanical properties in reinforced polymer composites

Synthetic hydroxyapatite (HA) whiskers have been utilized as a new, biocompatible reinforcement for orthopedic biomaterials. High-density polyethylene (HDPE) was reinforced with either the synthesized HA whiskers or a commercially available spherical HA powder using a novel powder processing technique that facilitated uniform dispersion of the reinforcements in the matrix prior to compression molding. Composites were processed for up to 60 vol % HA whiskers and up to 50 vol % spherical HA. The mechanical properties of the new composite biomaterials were examined by uniaxial tensile tests. As expected, increased volume fraction of either reinforcement type over 0-50 vol % resulted in increased elastic modulus, a maximum in ultimate tensile stress, and decreased work to failure. Composites reinforced with HA whiskers had higher elastic modulus, ultimate tensile strength, and work to failure relative to composites reinforced with spherical HA. Thus, HA whisker-reinforced HDPE composites possessed improved mechanical properties over those reinforced with spherical HA. HA whisker-reinforced composites were anisotropic due to alignment of the whiskers in the matrix during processing.

An investigation of fatigue crack nucleation and growth in a Ti–6Al–4V/TiB in situ composite

This paper presents the results of an experimental study of fatigue crack nucleation and growth in a Ti–6Al–4V/TiB in situ whisker-reinforced composite. The onset of crack nucleation is shown to correspond to ∼20% of the total life at a stress range of 480 MPa. This is associated with transverse cracking across TiB whiskers, and interfacial decohesion between the TiB whiskers and the Ti–6Al–4V matrix. Subsequent cracking occurs by the formation of multiple cracks across the elongated α grains. These cracks are retarded initially by the β phase. However, subsequent fatigue damage results in transgranular crack growth across α and β phases prior to the onset of catastrophic failure. The long fatigue crack growth rates in the Paris regime in the Ti–6Al–4V/TiB composite are comparable to those of Ti–6Al–4V processed under nominally identical conditions. However, the fatigue crack growth rates in the composite are faster than those in the matrix alloy at lower Δ K values. Cyclic deformation of the composite is associated with strain softening, presumably as a result of progressive interfacial decohesion around the TiB whiskers early in the fatigue deformation process. The implications of the results are assessed for potential structural applications of the Ti–6Al–4V/TiB composite.

On the Effects of Fiber Length and Spatial Distribution on the Stiffness of Short-Fiber Reinforced Composites

We report on the results of a computational investigation of the effect of fiber aspect ratio (ar) on the stiffness of composite rods reinforced with rigid spheroidal inclusions. The reinforcing spheroids are randomly placed within the containing rod and are also perfectly aligned with the tensile axis. Attention is focused in the interesting region of low (ar), where the stiffness of the composite rod is known to be most sensitive on (ar). Use of low aspect ratio fibers makes the results of this analysis suitable for a class of processed materials, such as whisker-reinforced metal-matrix composites and extruded or molded short-fiber-reinforced polymers. We consider steady-state three-dimensional deformations of composite rods containing up to 50 individual, randomly placed aligned spheroids. The equations of elasticity for the entire multi-fiber assembly are solved using the Boundary Element Method (BEM), implemented on a four-processor server and the force needed to impose a certain tensile deformation on the composite is computed. From this, an effective tensile modulus is obtained. Statistical averages of the computed effective moduli are compared to the predictions of the Mori-Tanaka model for the stiffness of short fiber composites. We find a good agreement at low values of (ar). Additionally, we investigate the effect on stiffness of random perturbations in fiber length around a mean value.